Posted 06/23/2016:
I like redundancy wherever I can get it, so in situations where I really am forced to use modern (narrow niche) parts inside of equipment, I purchase the inexpensive stuff so that I can have multiple units and redundancy in that way. So, my computers are all being shifted over to the very low cost ARM SoC varieties, and I’m currently in possession of four of them, obtained from various vendors.
Three of the four computers are self powered with NiMH batteries. I like the NiMH rather than the lithium tech for redundancy reasons. Most battery packs (be they lithium or NiMH) fail because one cell fails. So, to fix the battery packs (typically 8 – 10 NiMH cells) – in my little computers, I can replace one C or AA cell, and be back in business. All I need to do is have an extra couple 8 packs of the cells in a drawer, and I have a pretty good redundancy and backup system. With lithium packs, this could probably also be done, but for various reasons I see that battery technology as more complicated. The lithium packs are designed around critical parameters (to keep them from blowing up), and this might be disrupted by messing with the indivdual cells. I’m not the battery expert to say much about this, for sure. But, one of my other blogs has posts I’ve written about NiMH, and why I like that type of battery. It’s a personal preference, and is no endorsement by me to others. The NiMH are heavier, which is a turn-off to some people.
In some cases, the lithium packs would have to be disassembled (a safety concern), whereas the NiMH are all a very nice/simple “dry cell” type form factor. Don’t disassemble the lithium packs! This is not to say that NiMH batteries do not need to be respected, in terms of safety concerns (no batteries should be operated outside of their designs) – but again I’m not the battery expert to say for sure, so none of this is advice. I wouldn’t disassemble the power tool packs (neither lithium nor NiMH). The “insides” of an older NiMH based power tool will probably have a gang of NiMH AA cells, wrapped or glued together. This close proximity is one of the problems with those older battery packs, as excessive heat could damage one of the cells, rendering the whole pack useless. They sometimes had a thermistor on only one cell to monitor the heat (the batteries warmed in high demand applications such as drilling through a tough material), and that made problems more likely. My packs have thermistors on every cell. Like I said, it was often the failure of only one cell that ditched the whole pack. Anyway, I don’t disassemble power tool packs for the batteries, I just buy new. You never know how any battery pack is constructed internally, so as a caution I leave them alone for the most part. I did find that the “ganged batteries” in one of my NiMH power tool units had fairly low capacity/quality cells. I’m thinking it’s prudent and better to buy separates. Just an uneducated opinion.
The nice thing I’ve been noticing about NiMH, is that they are now available in department stores too – unlike the lithium battery cells. I’ve found that the department store variety typically has only half the capacity though. 😦 I’m a big Imedion brand battery fan, as I referenced on many of my programmingmiscellany.wordpress pages. The NiMH Imedions seem to be more consistent, in terms of the battery parameters, than some of the others, but I still “match” them to be very close to each other’s particular characteristics in my packs, and I use all sorts of circuits to protect against over/under voltages/currents/temperature/charge/etc. None of my brand preferences constitutes advice. The Imedions I purchase (“C” cells) have a capacity of five ampere hours. Yes – 5 Ah! For someone with LA gel cell and NiCad experience, that is really something. The “AA” cells have 2.5 Ah capacity.
NiMH batteries contain only about two thirds the energy of lithium IIRC, for the same volume of space, so you don’t typically find them in notebooks. Also, as I’ve mentioned, they’re a LOT heavier. Neither of those things is an issue for me though …
The NiMH is an older technology than lithium. NiMH was patented in 1987, and used in power tools (the battery operated drill motors that you could find in home improvement stores) until a few years ago, when lithium began completely taking over that battery market segment.
Getting back the the thread subject …
I already have an SDR shortwave method for retrieving weather faxes, using Quisk and FLDigi software. With a working Vanguard, I should have a second method. Then, it will be left to me to devise a way to retrieve the geo stationary (GHz) frequency weather facsimiles. With all three methods working, I’ll think I have enough redundancy. The few fangled way to get weather faxes is with Sirius, but that’s not my way of thinking at all :-).
Note: the author does not have a recent, applicable background in circuit building, or battery related issues, so this is presented as the work of a hobbyist, and is not meant for duplication by others. Readers should look elsewhere for design advice and info.
WB8LZR 